The biological effects of low doses of ionizing radiations are to be investigated within the framework of a biophysical theory. The determination of certain parameters should permit extrapolation of the dose effect curve to doses that are so low that it is impractical to determine effects experimentally. A variety of radiations are to be applied including neutrons of a wide range of energies, x and gamma rays and alpha radiation. The higher organisms irradiated will be principally mammals but insects and plants are to be used in certain studies. The effects under investigation include carcinogenesis, cell transformation, chromosome aberrations and genetic impairment.